Caught Off Guard in the Staff Room

I'm a high school teacher who's been in an open relationship for about six months now. My partner and I have agreed to explore casual encounters with others, which can be challenging given my job. Last week, I was in the staff room when someone new came in, let's call him Alex, and there was just this undeniable chemistry between us right away. We started talking, things got heated, and before we knew it, we were kissing passionately while everyone else was at lunch. It felt so spontaneous and intense, but now I'm worried about crossing professional lines. Is this something that happens to others in open relationships too? How do you navigate these feelings without compromising your integrity?